Technical Field
This invention relates to temporary maskants curable by actinic radiation for use in protecting metal substrates during grit blasting and plasma spray processing. The invention relates to a formulation capable of polymerization through exposure to actinic radiation that can be used to protect a metal substrate from high temperature and abrasive processing. These find use in the manufacture of such products as turbine blades, engine parts, circuit boards, one glass solution (OGS) and orthopedic replacement joints.
Description of the Related Art
The use of temporary radiation-curable masks in the processing of metal surfaces is well known. In many masking applications, two-part, solvent based or thermally cured maskants are impractical and uneconomical. Radiation curable masks can be applied easily and cured quickly using actinic radiation. U.S. Pat. No. 7,763,326 describes the process of applying and curing such a maskant in order to protect a metal surface during diffusion coating. These maskants provide sufficient protection of metal surfaces from processing such as anodizing, plating, and grit blasting, but cannot withstand the high temperatures of plasma spraying for extended periods of time. Current products use polymers having polyether, polyester or polybutadiene backbones which begin to deteriorate at high temperatures causing films to delaminate, blister, and break down.
U.S. Pat. No. 6,951,623 describes a method of protecting metal substrates from chemical exposure using a UV curable maskant. U.S. Pat. No. 5,420,171 is based on a maskant for protecting surface during soldering processes. The maskant is within a temperature of 510° F. for two second during soldering processing and then the film is removed by dissolving in water at a temperature of 120°-140° F. One must use a high temperature resistant tape in order to protect metal surfaces from processing at temperatures produced by plasma spray. Such a tape is described in U.S. Pat. No. 5,508,097. This taping process is manual and may take several hours to complete for each separate part. Tape delaminates during processes such as shot peening or grit blasting. This invention provides a maskant product that can be utilized to protect a metal substrate from both grit blasting and plasma spraying. The composition can be applied and cured within minutes, increasing efficiency and throughput. The mask can then be removed by either peeling or burning off at temperatures greater than 600° F. without leaving any substantial amount of residue. The invention provides a temporary maskant composition that includes a) a urethane (meth)acrylate oligomer having a polycarbonate or polycarbonate caprolactone backbone; b) a reactive diluent monomer capable of polymerization; c) a photoinitiator; d) an optional thickener and e) other optional additives. These compositions are applied to a surface that is to be protected, for example, a surface that has to be protected from grit blasting and/or plasma spray. Thereafter, these compositions are cured by exposing them to actinic radiation. These maskants find use as surface protectants in industrial processes such as acid stripping, anodizing, plating, chemical milling, grit blasting, shot peening, vibratory finishing, air plasma spraying, painting and powder coating. However, they find most particular use in protecting metal surfaces from high temperature treatments for extended periods of time while retaining their removability. The maskant must then be able to withstand temperatures of up to about 600° F. for up to about 30 minutes without delaminating from the metal substrate and still retain enough flexibility and tensile strength such that it would be peelable for removal. After processing, the maskant can be removed by peeling or burning off at temperatures greater than 600° F.